Purchasers of state of the art home and portable audio systems expect improved audio performance, as well as more options for controlling playback from the given recording media. One of the most important performance criteria is the elimination of clicks, pops, noise and other artifacts audible to the listener. Not only are these audible artifacts distracting, but they can also damage the system speakers or headset. This problem is especially true with transient artifacts, such as clicks and pops, which may spike the output signal driving the speakers or headset to a relatively high level.
Clicks and pops can be caused by a number of different conditions. One particular situation when clicks and pops arise in digital audio systems is during power transitions, such as during system power-up or power-down. Typically, the analog to digital converter (DAC) stage, which converts the digital audio input stream to analog form, is coupled through a capacitor to the following analog processing circuitry. During power transitions, the stored charge on this coupling capacitor must be discharged slowly to ensure that a voltage spike is not passed to the analog processing circuitry, which would otherwise convert the voltage spike into an audible click or pop.
While there are presently a number of different techniques for controlling clicks and pops, including the control of clicks and pops in audio analog to digital converters, these techniques adversely impact other aspects of system performance. Consequently, new circuits and methods are needed which control clicks, pops without significantly impacting other aspects of system performance.